The subject matter of the present invention is a method and a device for the non-destructive inspection of a rotationally symmetric workpiece having sections with different diameters by means of a non-destructive inspection technique, such as ultrasound, eddy currents or X-rays. An ultrasonic inspection in accordance with the pulse echo method is used with particular preference as the inspection technique. In a particularly development, the method and the device are suited, in particular, for the inspection of a workpiece with an anisotropic sound velocity. For example, an anisotropic sound velocity is frequently observed, for example, in forged solid shafts which can be used, for instance, in rail vehicles.
The non-destructive inspection of rotationally symmetric workpieces having sections with different diameters by means of non-destructive inspection techniques often suffers from the problem of the geometrical structure of the workpiece causing geometry-related signals of the inspection technique used. These signals are correlated with the geometry of the workpiece, which is already known as such, and therefore frequently do not contain any further information. Furthermore, these so-called “geometry echoes” in many cases have a very high amplitude. There is therefore the possibility of the intensive geometry echoes obscuring less intensive underlying signals that could be correlated with, for example, flaws to be detected in the workpiece. Due to the limited dynamics of the signal processing used within the context of the inspection technique, there is therefore a danger of geometric echoes “masking” relevant signals, e.g. flaw signals.
This issue is of particular relevance, for example, in the inspection of wheel sets of rail vehicles by means of ultrasound. Wheel sets of rail vehicles generally include one pair of wheels mounted on a rigid solid or hollow shaft. The shafts used in this case often have external diameters changing from section to section, for example defined regions for the accommodation of functional components, such as the wheels, anti-friction bearings or brake disks. It is obvious that the shafts of wheel sets of rail vehicles constitute safety-relevant components that are subject to natural wear over the long life span of rail vehicles. For this reason, their freedom from flaws has to be determined by means of non-destructive inspection methods not only during the production of wheel sets for rail vehicle. Rather, a regular inspection with regard to freedom from flaws of all components, in this case particularly the wheels as well as the shaft used, is required also over the entire life span of a wheel set. In practice, the most frequent wear phenomenon observed in shafts of wheel sets of rail vehicles is the occurrence of incipient cracks, i.e. crack-like fatigue failures that start at the surface of the respective shaft. Every rail vehicle operator therefore has to provide suitable inspection methods and devices in order to check the wheel sets of rail vehicles with regard to their freedom from flaws regularly.
Until this day, the inspection by means of ultrasound of rotationally symmetric workpieces having diameters that change from section to section, in particular of solid shafts of rail vehicles, constitutes a particularly challenging inspection task. This is based, in particular, on the fact that intensive geometry echoes, which can be superposed over the signals of the flaws to be detected, are observed in the ultrasonic inspection of rotationally symmetric workpieces having diameters that change from section to section.
Moreover, the inspection of a wheel set of a rail vehicle often entails a downtime of the rail vehicle, which is directly connected to high downtime costs due to the rail vehicle being out of service. In order to minimize them, it would be desirable to be able to inspect a fully assembled wheel set, i.e. a wheel set with assembled bearings and/or brake disks. If they are mounted, then an insonification from the shaft or from the end face (e.g. by means of a conical probe) is not possible with the ultrasound-based inspection methods known from the prior art.
Finally, the generation of an easily interpreted representation of the results of, for example, an ultrasound inspection obtained on a rotationally symmetric workpiece constitutes a problem which, as far as the applicant is aware, has so far been solved only to an insufficient extent.